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Spring Suspension System in Automobile | Leaf Spring Suspension System | Leaf, Coil and Torsion Springs in Suspension System



Leaf spring a type of spring suspension system in automobile also denoted to as semi-elliptical springs are one of the ancient form of suspension used in vehicles, particularly heavy vehicles. A leaf spring appears like a bow minus the string. It contains of a stack of curved narrow plates of the same width and varied length clamped together with shorter plates at the center to form a semi-elliptical shape. The center of the arc delivers location for the axle, tie holes are made available at either end for getting attached to the body.


Any spring, maybe it’s a leaf, torsion or coil spring, must compensate for irregularities in the road surface, keep the suspension system at a fixed height and support added weight without excessive sagging. Each of those works is very significant in providing comfort, specific handling and load-bearing ability in the modern vehicle – three key areas that will raise customer concerns.


In ancient times the steel multi-leaf spring is one of the first-born and most widely used spring designs in suspension systems. The leaf spring have many advantages, not only it acts as a spring, but also because it attaches the axle straight to the chassis.

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There are two varieties of leaf springs. They are the mono-leaf springs and the multi-leaf springs. As the name proposes, the mono-leaf suspension involves of a single link. They are thick in the middle and narrowing out at the end. It does not offer much strength and suspension to dragged vehicles.


Multi-leaf springs are mainly used for heavier vehicles which offer increased strength and suspension. The recent development in design is the parabolic leaf spring. It can contain a mono-leaf or multi-leaf configuration. It has less leaves in comparison to the semi-elliptical multi-leaf springs whose thickness differs from center to the end and it follows a parabolic path. This shape not only saves weight but also provides greater flexibility which improves ride quality. A trade-off of using parabolic leaf spring is reduced load carrying capability.



Torsion-bar suspensions have been used for many years on vehicles provided with short-long-arm (SLA) suspension systems. As the name implies, the torsion bar is basically a round bar, about four feet long, that’s designed to twist as weight is applied to the suspension system. Since a torsion bar is usually preloaded by a clockwise or counterclockwise coil constructed into it, a torsion bar will fit on the side of the vehicle for which it was de­signed.

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The benefits of the torsion bar suspension system inc­lude compactness and light weight. Since the torsion bar tension is measured by a threaded screw adjustment, torsion bars can be used to tune suspension height. Besides, torsion bars can be attached either to the upper or lower control arms, aggregating the versatility of the design.


The function of a coil spring can be well understood if we imagine it as a long, thin, torsion bar twisted into a coil shape. Because the coiled wire twists through the spring’s compression/extension cycles, the coil spring essentially functions on the same principle as a torsion bar.


As a coil spring occupies a relatively small space, it can be used in a most types of suspension designs including MacPher­son strut, solid axle with trailing arms, independently sprung rear axle, or any SLA suspension system using a spring or coil-over shock absorber configuration.

Most recent imports use the coil spring in differences of the MacPherson strut design. In common, wire gauge, length, overall diameter and numbers of coils control the characteristics of the coil spring.

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Sometimes a coil spring can be considered as a variable rate spring that increases load-bearing capability as it’s compressed. Flexible rate coil springs are often used in chassis configurations that rarely carry heavy loads.


1) The manufacture of the suspension is simple and strong as it performances as a linkage for holding the axle in place and thus a separate linkage isn’t necessary.
2) As they detect the rear axle, the need for trailing arms and panhard rod is removed, thus saving cost and weight.
3) It provisions the weight of the chassis.
4) It controls chassis roll more proficiently by utilizing a higher rear moment center and a wider spring base.


1) The leaf-spring systems are difficult to install.
2) The inter-leaf friction between the leaf springs decreases the ride comfort.
3) The leaf springs may be apt to to lose shape and sag over time. 4) Acceleration and braking torque roots wind-up and vibration. Also wind-up causes rear-end squat and nose-diving.

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